The terra cotta tiles were originally fired at an extremely high temperature. They'll withstand an oven. Any stone or tile could crack if it is susceptible to drastic temperature changes or moisture. Never get a stone wet and don't take a hot stone out of an oven. The whole idea of stones is to retain heat and why many of us will pre-heat a stone 30 minutes or more before putting a pizza in. So taking the stone out with the pizza and trying to bake a second pizza defeats the pre-heat concept and does abruptly change the temperature. Spraying a stone can change its temperature and induce stress. Wetting down or washing a stone can also cause it to retain moisture that is not visually apparent and stress it under high heat. I never wet a stone. I clean my stone between use with a paint scraper and have had great success thoroughly cleaning a stone by leaving it in the oven when cleaning the oven. I haven't cracked mine yet after three years of use.
